Recently, the tasks a robot is to perform (operations of the robot) at an actual place of installation are set by off-line teaching so as to shorten the time required for setting the robot at the actual place of installation.
In the off-line teaching, a model of the robot, a model of equipment around the robot at the place of installation, a model of a workpiece and the like are set in a simulation device, and an operation program for the robot at the place of installation is made in the simulation device.
An actual position of the distal end portion of the robot is slightly different from the position of the distal end portion of the robot which is calculated by the simulation device due to assembly errors, the influence of gravity or the like. Such differences vary depending on the size of the robot, the weight of the workpiece which is manipulated by the robot and the like, and the differences may be approximately 5 mm in some cases. For this reason, when the robot is operated at the place of installation by the operation program, which is made by off-line teaching, without any modifications, failures may occur.
For the reasons above, the difference between the position of the distal end portion of the robot at the place of installation and a position which is intended by the operation program is measured, and correction (calibration) of the operation program is performed based on the measurement result.
A measurement system for measuring the position of a distal end portion of a robot is known, and the measurement system uses a measuring apparatus for measuring a position of a reflector unit (see Japanese Unexamined Patent Application, Publication No. 2017-019072, for example). This reflector unit has three shafts fixed at the distal end portion of the robot such that longitudinal axes of the shafts make right angles to each other, and six reflectors which are respectively mounted at both ends of the shafts.